1. Field of the Invention
This invention relates in general to the construction of molds and in particular to a new and useful device for regulating the flow of moldable material from a vent passage of a mold.
2. Description of the Prior Art
The present invention relates particularly to shut-off mechanism for closing a vent passage of a casting mold as a function of the degree of filling of the mold. The closing of the vent passage is intended as a precaution for preventing the liquid casting material from entering into the vacuum producing device which aids in the venting of the mold or in order to prevent the material from escaping to the outside. During the venting in a casting mold it is important to allow for a sufficient time for venting in order to avoid inclusions of air in the cast material. This however requires a rapid closing of the vent passage and as soon as possible after the cast material has penetrated therein. Many solutions have been proposed for accomplishing this including a shut-off mechanism of a type which employs a control piston which acts on a lever system connected to a valve and in a system in which there are two separate parallel vent passages of which one leads to the control piston and the other to the valve. Such an arrangement the lever system is necessary because the control piston under pressure of the casting material travels only a small distance due to its disadvantageous positioning. Another drawback of such a shut-off mechanism is that the control piston is displaced only after a sufficiently high pressure builds up at its working surface. This results in a time delay which disadvantageously affects the instantaneous closing of the valve. In addition this parallel arrangement of the control piston and valve does not insure that in each case the casting material will reach first the control piston and not the valve.
In another shut-off mechanism that is known the control piston and the shut-off mechanism are mounted in series so that the casting material reaches first the control piston and only later the shut-off mechanism. In such case the control piston is positioned so tht it is actuated only after a sufficiently high pressure has been built up. In order to shorten the switching time the control piston does not switch directly the shut-off mechanism but only an additional source of energy acting on the shut-off mechanism and it operates in the particular known case on a valve designed as an amplifier and/or a converter. Such a design of the shut-off mechanism is complicated and expensive in manufacture and also due to the plurality of individual parts and numerous connections it is susceptible to very many operating difficulties.
Another known shut-off mechanism includes a control piston having a working surface on which the cast material flowing into the vent passage impinges so that the control piston is moved from its initial position into a closing position. The vent passage extends adjacent to the mold parting surface along the control piston up to a location where the vent passage is interrupted because of the displacement of the control piston. With such a construction not only the static pressure which is predominant in the cast material flow but also the kinetic energy of the material flow is utilized for actuating the control piston. This results in obtaining a longer stroke of the control piston or a shorter switching time. Additional auxiliary sources of energy controlled by the control piston and then acting on the shut-off mechanism become superfluous and with this arrangement of the control piston. The travel of the control piston is so long that it can be used for directly actuating the usual shut-off mechanism such as a valve or gate valve. However this more simple construction has not proved satisfactory.